The chloride process for producing titanium dioxide is well known, see Volume 24 of the Kirk-Othmer Encyclopedia of Chemical Technology (4th Ed., 1997) and in Volume I of the Pigment Handbook, Edited by Lewis (2nd Ed., 1988). The first step of the chloride process for producing titanium dioxide is the chlorination of a titanium bearing material (for example, rutile ore) in a fluidized bed reactor, see U.S. Pat. Nos. 2,701,179; 2,790,703; 3,526,477; 3,883,636; 3,591,333; 4,046,854; 4,619,815; 4,854,972; 4,961,911; 5,389,353; 5,670,121; and 5,585,078 (all of which are fully incorporated herein by reference). In summary, the titanium bearing material, a source of carbon (usually coke) and chlorine are reacted (for example at 900–1300 degrees Celsius) in a fluidized bed at the lower portion of the reactor to produce a gaseous stream comprising titanium tetrachloride, carbon monoxide; carbon dioxide and carbonyl sulfide, which gaseous stream moves to the upper portion of the reactor and then is exhausted from the reactor for further processing.
According to the teachings of the above-referenced '121 patent: (a) it is desirable in such a reactor to minimize the formation of carbon monoxide to decrease the amount of carbon required per unit of titanium tetrachloride produced; and (b) it is desirable to decrease the formation of carbonyl sulfide because carbonyl sulfide is an undesired byproduct. According to the teachings of the '121 patent, the formation of carbon monoxide and carbonyl sulfide can be reduced by cooling the fluidized bed, such as by introducing a suitable cooling material (such as titanium tetrachloride at 100 degrees Celsius) into the reactor above the fluidized bed. However, according to the teachings of the '121 patent, if the fluidized bed is overcooled, then the concentration of unreacted chlorine tends to increase to undesirable levels in the gaseous stream from the reactor. Thus, there appears to be an optimum temperature of the fluidized bed in the reactor which temperature can be controlled by, for example, controlling the amount of cooling material introduced into the reactor above the fluidized bed. According to the teachings of the above-referenced '911 patent, chlorine can be added just above the surface of the fluidized bed to convert carbon monoxide to carbon dioxide. According to the teachings of the above-referenced '078 patent, oxygen can be added to the reactor to convert carbon monoxide to carbon dioxide and to convert carbonyl sulfide to sulfur dioxide.
With the above in view, it is apparent that a number of different improvements have been made to the fluidized bed process for converting titanium dioxide to titanium tetrachloride so that the concentration of undesirable byproducts of the process can be reduced. For example, formation of undesirable carbon monoxide can be reduced and/or carbon monoxide can be converted to carbon dioxide. And, the formation of undesirable carbonyl sulfide can similarly be reduced and/or the carbonyl sulfide can be converted to sulfur dioxide. Whatever improved process is used to reduce the concentration of undesirable components (such as carbon monoxide and/or carbonyl sulfide) the gaseous exhaust stream from the reactor can be analyzed to control the improved process. For example, the '121 patent disclosed the use of a Fourier transform infrared analyzer to analyze the exhaust gas stream from the reactor (after the titanium tetrachloride was condensed therefrom) for carbonyl sulfide.
Analysis of the exhaust gas stream from the reactor is difficult because the stream is hot, corrosive and contains particulates. Analysis of the exhaust gas stream after the titanium tetrachloride has been condensed therefrom is more favorable but still problematic because, for example, the required sampling systems tend to corrode and plug. It would be an advance in the art of chemical analysis of the gasses from a fluidized bed reactor for making titanium tetrachloride if components therein (such as carbon monoxide, carbon dioxide, carbonyl sulfide and sulfur dioxide) could be determined without the need to extract a sample thereof and especially if the determination were related to a concentration ratio of one undesired component to another related more desirable component (such as the concentration ratio of carbon monoxide to carbon dioxide or the concentration ratio of carbonyl sulfide to sulfur dioxide).